Sputtering methods for depositing stress tunable tantalum and tantalum nitride films

ABSTRACT

The present disclosure pertains to our discovery that residual stress residing in a tantalum film or tantalum nitride film can be controlled (tuned) by controlling particular process variables during film deposition. By tuning individual film stresses within a film stack, it is possible to balance stresses within the stack. Process variables of particular interest include: power to the sputtering target; process chamber pressure (i.e., the concentration of various gases and ions present in the chamber); substrate DC offset bias voltage (typically an increase in the AC applied substrate bias power); power to an ionization source (typically a coil); and temperature of the substrate upon which the film is deposited. The process chamber pressure and the substrate offset bias most significantly affect the film tensile and compressive stress components, respectively. The most advantageous tuning of a sputtered film is achieved using high density plasma sputter deposition, which provides for particular control over the ion bombardment of the depositing film surface. When the tantalum or tantalum nitride film is deposited using high density plasma sputtering, power to the ionization source can be varied for stress tuning of the film. We have been able to reduce the residual stress in tantalum or tantalum nitride films deposited using high density plasma sputtering to between about 6×10 +9  dynes/cm 2  and about -6×10 +9  dynes/cm 2  using techniques described herein. The tantalum and tantalum nitride films can also be tuned following deposition using ion bombardment of the film surface and annealing of the deposited film.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to tantalum and tantalum nitride filmswhich can be stress tuned to be in tension or in compression or to havea particularly low stress, and to a method of producing such films.These stress tuned films are particularly useful in semiconductorinterconnect structures where they can be used to balance the stresswithin a stack of layers which includes a combination of barrier layers,wetting layers, and conductive layers, for example. The low stresstantalum and tantalum nitride films are particularly suited for thelining of vias and trenches having a high aspect ratio.

2. Brief Description of the Background Art

A typical process for producing a multilevel structure having featuresizes in the range of 0.5 micron (μm) or less would include: blanketdeposition of a dielectric material; patterning of the dielectricmaterial to form openings; deposition of a diffusion barrier layer and,optionally, a wetting layer to line the openings; deposition of aconductive material onto the substrate in sufficient thickness to fillthe openings; and removal of excessive conductive material from thesubstrate surface using a chemical, mechanical, or combinedchemical-mechanical polishing techniques. Future technologicalrequirements have placed a focus on the replacement of aluminum (andaluminum alloys) by copper as the conductive material. As a result,there is an increased interest in tantalum nitride barrier layers and intantalum barrier/wetting layers which are preferred for use incombination with copper.

Tantalum nitride barrier films, Ta₂ N and TaN, have been shown tofunction up to 700° C. and 750° C., respectively, without the diffusionof copper into an underlying silicon (Si) substrate. Tantalumbarrier/wetting films have been shown to function at temperatures ofapproximately 500° C. It is advantageous in terms of processingsimplicity to sputter the barrier and or wetting layers underlaying thecopper. Tantalum nitride barrier layers are most commonly prepared usingreactive physical sputtering, typically with magnetron cathodes, wherethe sputtering target is tantalum and nitrogen is introduced into thereaction chamber.

S. M. Rossnagel and J. Hopwood describe a technique which enablescontrol of the degree of directionality in the deposition of diffusionbarriers in their paper titled "Thin, high atomic weight refractory filmdeposition for diffusion barrier, adhesion layer, and seed layerapplications" J. Vac. Sci. Technol. B 14(3), May/June 1996. Inparticular, the paper describes a method of depositing tantalum (Ta)which permits the deposition of the tantalum atoms on steep sidewalls ofinterconnect vias and trenches. The method uses conventional,non-collimated magnetron sputtering at low pressures, with improveddirectionality of the depositing atoms. The improved directionality isachieved by increasing the distance between the cathode and theworkpiece surface (the throw) and by reducing the argon pressure duringsputtering. For a film deposited with commercial cathodes (AppliedMaterials Endura® class; circular planar cathode with a diameter of 30cm) and rotating magnet defined erosion paths, a throw distance of 25 cmis said to be approximately equal to an interposed collimator of aspectratio near 1.0. In the present disclosure, use of this "long throw"technique with traditional, non-collimated magnetron sputtering at lowpressures is referred to as "Gamma sputtering".

Gamma sputtering enables the deposition of thin, conformal coatings onsidewalls of a trench having an aspect ratio of 2.8:1 for 0.5 μm-widetrench features. However, we have determined that Gamma sputtered TaNfilms exhibit a relatively high film residual compressive stress, in therange of about -1.0×10⁺¹⁰ to about -5.0×10⁺¹⁰ dynes/cm². High filmresidual compressive stress, in the range described above can cause a Tafilm or a tantalum nitride (e.g. Ta₂ N or TaN) film to peel off from theunderlying substrate (typically silicon oxide dielectric). In thealternative, the film stress can cause feature distortion on thesubstrate (typically a silicon wafer) surface or even deformation of athin wafer.

A method of reducing the residual stress in a Ta barrier/wetting film ora Ta₂ N or TaN barrier film would be beneficial in enabling theexecution of subsequent process steps without delamination of such filmsfrom trench and via sidewalls or other interconnect features. Thisreduces the number of particles generated, increasing device yieldduring production. In addition, a film having a near zero stresscondition improves the reliability of the device itself.

SUMMARY OF THE INVENTION

We have discovered that the residual stress residing in a tantalum (Ta)film or a tantalum nitride (TaN_(x), where 0<×≦1.5) film can becontrolled (tuned) by controlling particular process variables duringdeposition of the film. Process variables of particular interest forsputter applied Ta and TaN_(x) films include the following. An increasein the power to the sputtering target (typically DC) increases thecompressive stress component in the film. An increase in the processchamber pressure (i.e. the concentration of various gases and ionspresent in the chamber) increases the tensile stress component in thefilm. An increase in the substrate DC offset bias voltage (typically anincrease in the applied AC as substrate bias power) increases thecompressive stress component in the film. The substrate temperatureduring deposition of the film also affects the film residual stress. Ofthese variables, an increase in the process chamber pressure and anincrease in the substrate offset bias most significantly affect thetensile and compressive stress components, respectively. The mostadvantageous tuning of a sputtered film is achieved using Ion MetalPlasma (IMP) as the film deposition method. This sputtering methodprovides for particular control over the ion bombardment of thedepositing film surface. When it is desired to produce a film havingminimal residual stress, particular care must be taken to control theamount of ion bombardment of the depositing film surface, as an excessof such ion bombardment can result in an increase in the residualcompressive stress component in the deposited film.

Tantalum (Ta) films deposited using the IMP method typically exhibit aresidual stress ranging from about +1×10⁺¹⁰ dynes/cm² (tensile stress)to about -2×10⁺ dynes/cm² (compressive stress), depending on the processvariables described above. Tantalum nitride (TaN_(x)) films depositedusing the IMP method typically can be tuned to exhibit a residual stresswithin the same range as that specified above with reference to Tafilms. We have been able to reduce the residual stress in either the Taor TaN_(x) films to low values ranging from about +1×10⁺⁹ dynes/cm² toabout -2×10⁺⁹ dynes/cm² using tuning techniques described herein. Thesefilm residual stress values are significantly less than those observedfor traditionally sputtered films and for Gamma-sputtered films. Thisreduction in film residual compressive stress is particularly attributedto bombardment of the film surface by IMP-generated ions during the filmdeposition process. Heavy bombardment of the film surface byIMP-generated ions can increase the film residual compressive stress, sowhen it is desired to minimize the film compressive stress, the ionbombardment should be optimized for this purpose.

Other process variables which may be used in tuning the film stressinclude the spacing between the sputter target and the substrate surfaceto be sputter deposited; ion bombardment subsequent to film deposition;and annealing of the film during or after deposition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the residual stress in an IMP deposited Tafilm as a function of DC power to the Ta target, RF power to the IMPionization coil, and the pressure in the process chamber.

FIG. 2A is a contour plot showing the IMP deposited Ta film residualstress in dynes/cm² as a function of the DC power to the Ta target andthe process chamber pressure, when the RF power to the ionization coilis 1 kW.

FIG. 2B is a contour plot showing the residual stress in an IMPdeposited Ta film as a function of the same variables illustrated inFIG. 2A, when the RF power to the ionization coil is 3 kW.

FIG. 3 is a graph showing the residual stress in an IMP deposited Tafilm as a function of the substrate offset bias, and in particular as afunction of the AC bias power (typically the AC power is coupled to thesubstrate through the substrate heater which is in electrical contactwith the substrate).

FIG. 4 is a graph showing the chemical composition of a Gamma-sputteredtantalum nitride film, as a function of the nitrogen gas flow rate tothe sputtering process chamber. In addition, FIG. 4 shows theresistivity and the structure of the tantalum nitride compound, which isin conformance with the nitrogen content of the compound.

FIG. 5 is a graph showing the film composition of a reactiveIMP-deposited tantalum nitride film, as a function of the nitrogen gasflow rate to the process chamber. Again, the resistivity of the film isindicative of the various film structures created as the nitrogencontent of the film is increased.

FIG. 6 is a graph showing the residual film stress for Gamma-sputteredtantalum nitride film as a function of the nitrogen gas flow rate to thesputtering process chamber and as a function of the temperature at whichthe film is deposited.

FIG. 7 is a graph showing the residual film stress for reactive IMPsputtered tantalum nitride film as a function of the nitrogen gas flowrate to the sputtering process chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention pertains to stress tunable tantalum and tantalumnitride films and to a method of producing such films. In particular,applicants have discovered that residual film stress can be tuned bycontrolling particular process variables such as process chamberpressure, DC offset bias voltage, power to the sputtering target andsubstrate temperature during film deposition. When IMP sputtering isused, a variation in the power to the ionization coil can be used fortuning. Ion bombardment of the depositing film surface is particularlyuseful in controlling residual film stress.

I. Definitions

As a preface to the detailed description, it should be noted that, asused in this specification and the appended claims, the singular forms"a", "an", and "the" include plural referents, unless the contextclearly dictates otherwise. Thus, for example, the term "asemiconductor" includes a variety of different materials which are knownto have the behavioral characteristics of a semiconductor, reference toa "plasma" includes a gas or gas reactants activated by an RF glowdischarge, and reference to "copper" includes alloys thereof.

Film stress values were measured using a Tencor® Flexus FLX 3200 machineavailable from Tencor Corporation, Mountain View, Calif.

Specific terminology of particular importance to the description of thepresent invention is defined below.

The term "aspect ratio" refers to the ratio of the height dimension tothe width dimension of particular openings into which an electricalcontact is to be placed. For example, a via opening which typicallyextends in a tubular form through multiple layers has a height and adiameter, and the aspect ratio would be the height of the tubulardivided by the diameter. The aspect ratio of a trench would be theheight of the trench divided by the minimal travel width of the trenchat its base.

The term "completely filled" refers to the characteristic af a featuresuch as a trench or via which is filled with a conductive material,wherein there is essentially no void space present within the portion ofthe feature filled with conductive material.

The term "copper" refers to copper and alloys thereof, wherein thecopper content of the alloy is at least 80 atomic % copper. The alloymay comprise more than two elemental components.

The term "feature" refers to contacts, vias, trenches, and otherstructures which make up the topography of the substrate surface.

The term "Gamma or (γ) sputtered copper" refers to the "long throw"sputtering technique described in the paper by S. M. Rossnagel and J.Hopwood, which was discussed previously herein. Typically the distancebetween the substrate and the target is about the diameter of thesubstrate or greater; and, preferably, the process gas pressure issufficiently low that the mean free path for collision within theprocess gas is greater than the distance between the target and thesubstrate.

The term "ion metal plasma" or "IMP" refers to sputter deposition,preferably magnetron sputter deposition (where a magnet array is placedbehind the target). A high density, inductively coupled RF plasma ispositioned between the sputtering cathode and the substrate supportelectrode, whereby at least a portion of the sputtered emission is inthe form of ions at the time it reaches the substrate surface.

The term "IMP sputtered tantalum" refers to tantalum which was sputteredusing the IMP sputter deposition method.

The term "IMP sputtered tantalum nitride" refers to tantalum nitridewhich was sputtered using the IMP sputter deposition method.

The term "reactive IMP sputtered tantalum nitride" refers toion-deposition sputtering wherein nitrogen gas is supplied during thesputtering of tantalum, to react with the ionized tantalum, producing anion-deposition sputtered tantalum nitride-comprising compound.

The term "stress tuned" refers to a TaN_(x) or Ta film which has beentreated during processing to adjust the residual stress within thedeposited film to fall within a particular desired range. For example,at times it is desired to use the TaN_(x) or Ta film to balance theoverall stress within a stack of layers, so the film may be tuned to bein compression or tension. At other times it may be desired to reducethe stress in the film to be as near to zero as possible.

The term "traditional sputtering" refers to a method of forming a filmlayer on a substrate wherein a target is sputtered and the materialsputtered from the target passes between the target and the substrate toform a film layer on the substrate, and no means is provided to ionize asubstantial portion of the target material sputtered from the targetbefore it reaches the substrate. One apparatus configured to providetraditional sputtering is disclosed in U.S. Pat. No. 5,320,728, thedisclosure of which is incorporated herein by reference. In such atraditional sputtering configuration, the percentage of target materialwhich is ionized is less than 10%, more typically less than 1%, of thatsputtered from the target.

II. An Apparatus For Practicing the Invention

A process system in which the method of the present invention may becarried out is the Applied Materials, Inc. (Santa Clara, Calif.) Endura®Integrated Processing System. The system is shown and described in U.S.Pat. No. 5,186,718, the disclosure of which is hereby incorporated byreference.

The traditional sputtering process is well known in the art. The Gammasputtering method is described in detail by S. M. Rossnagel and J.Hopwood in their paper titled "Thin, high atomic weight refractory filmdeposition for diffusion barrier, adhesion layer, and seed layerapplications", as referenced above. The IMP sputtering method is alsodescribed by S. M. Rossnagel and J. Hopwood in their paper "Metal iondeposition from ionized magnetron sputtering discharge, J. Vac. Sci.Technol. B, Vol. 12, No. 1 (January/February 1994).

III. The Structure of the Tantalum and Tantalum Nitride Films

We have been able to create a copper filled trench or via, which iscompletely filled, at a feature size of about 0.4 μ and an aspect ratioof greater than 1:1 (up to about 3:1 presently). To facilitate the useof a copper fill, the trench or via (constructed in a silicon oxidesurface layer) was lined with a reactive IMP sputtered TaN_(x) barrierlayer, followed by a Ta barrier/wetting layer, to create a bilayer overthe oxide surface layer. The copper fill layer was applied using asputtering technique in the manner described in applicants' co-pendingU.S. application Ser. No. 08/855,059, filed May 13, 1997, pending.

To ensure the overall dimensional stability of the structure, weinvestigated various factors which affect the residual film stress in aTaN_(x) barrier layer and in a Ta layer (which can serve as a barrierlayer, a wetting layer, or both, depending on the application).

One skilled in the art can envision a combination of a number ofdifferent layers underlaying the copper fill material. Whatever thecombination of layers, they provide a stack of layers; and tuning thestress of individual layers within the stack can provide a more stressbalanced and dimensionally stable stack. Although the preferredembodiment described above is for the lining of trenches and vias, oneskilled in the art will appreciate that the stress tuned TaN_(x) and Tafilms described herein have general application in semiconductorinterconnect structures. The method of controlling and reducing theresidual film stress in tantalum nitride and tantalum films can be usedto advantage in any structure in which a layer of such a film ispresent. The concept of tuning the residual stress in asputter-deposited film comprising at least one metal element has broadapplicability.

IV. The Method of Tuning Residual Stress in Tantalum and TantalumNitride Films

The preferred embodiments described herein were produced in an Endura®Integrated Processing System available from Applied Materials of SantaClara, Calif. The physical vapor deposition (sputtering in this case)process chamber is capable of processing an 8 inch (200 mm) diametersilicon wafer. The substrate was a silicon wafer having a silicon oxidesurface coating with trenches in the surface of the silicon oxide.Sputtering was carried out using a tantalum target cathode havingapproximately a 35.3 cm (14 in.) diameter, and DC power was applied tothis cathode over a range from about 1 kW to about 18 kW. The substratewas placed at a distance of about 25 cm (9.8 in.) from the tantalumtarget cathode in the case of gamma sputtering, and at a distance ofabout 14 cm (5.5 in.) from the cathode in the case of IMP sputtering.During IMP sputtering, an AC bias power ranging from about 0 W to about400 W was applied to the substrate, to produce a substrate offset biasranging from about 0 V to about -100 V. The substrate offset biasattracts ions from the plasma to the substrate.

Example One

When Gamma-sputtered tantalum film was produced, the film was sputteredusing conventional (traditional) magnetron sputtering, with rotatingmagnet-defined erosion paths (for better uniformity and cathodeutilization). Two hundred (200) mm sample surfaces weresputter-deposited at a sample surface temperature of about 25° C., inargon, at pressures of about 1.5 mT or less. The cathode to sample or"throw" distance was typically about 25 cm. The DC power to the tantalumtarget was approximately 4 kW. No substrate offset bias was used. Underthese conditions, the residual film stress of the tantalum film wasabout -1.5×10⁺¹⁰ dynes/cm².

Example Two

When IMP-sputtered tantalum film was produced, a high density,inductively coupled RF plasma was generated in the region between thetarget cathode and the substrate by applying RF power to a coil (havingfrom 1 to 3 turns) over a range from about 400 kHz to about 13.56 MHz(preferably about 2 MHz). Two hundred (200) mm sample surfaces were IMPsputter-deposited at a sample surface temperature of about 25° C., inargon, at pressures ranging from about 10 mT to about 60 mT. Thedistance from the cathode to the sample was typically about 14 cm. TheDC power to the tantalum target was adjusted over a range from about 1kW to about 8 kW (preferably about 1 kW to about 3 kW). The wattage tothe RF power coil was adjusted over a range from about 1.0 kW to about 5kW (preferably about 1.0 kW to about 3 kW). An AC bias power rangingfrom about 0 W to about 500 W was used. FIG. 1 shows a graph 100 of theresidual film stress 101 of the tantalum film in dynes/cm², as afunction of the RF power 108 to the ionization coil, as illustrated bythe curve numbered 102; the pressure 110 in the sputtering chamber, asillustrated by the curve numbered 104; and the DC power 112 to thesputtering target (cathode), as illustrated by the curve numbered 106.

As indicated in graph 100, the residual stress in the deposited Ta filmcan be tuned over a wide range, for example (but not by way oflimitation), from about 1.0×10⁺¹⁰ dynes/cm² to about -2×10⁺¹⁰ dynes/cm²,and can be set at a low stress nominal value, for example, between about6×10⁺⁹ dynes/cm² and about -6×10⁺⁹ dynes/cm², a range over which theresidual stress can approach zero. At a residual stress of about -6×10⁺⁹dynes/cm², by way of example, the IMP sputtered film residualcompressive stress is a factor of three lower than the residualcompressive stress of a typical gamma-sputtered Ta film. The processvariables which affect film residual stress can be optimized to producethe desired residual film stress in Ta films.

FIGS. 2A and 2B show the effect of an increase in the RF power to theIMP ionization coil, which is directly related to the amount of ionbombardment at the tantalum film surface. FIG. 2A, graph 200, shows theTa residual film stress in curves 201 through 206, when the power to theionization coil is 1 kW, as a function of process chamber argon pressure207 and the DC power to the tantalum target 208. FIG. 2B, graph 220,shows the Ta residual film stress interior of ellipses 221 and 222, whenthe power to the ionization coil is 3 kW, as a function of processchamber argon pressure 227 and the DC power to the tantalum target 228.

These curves show that, with the other process values held constant, anincrease in RF power to the ionization coil from 1 kW to 3 kW results inan increase in the film residual compressive stress. Even so, under allof the process conditions shown, the residual film stress for theIMP-sputtered tantalum is less than that of a Gamma-sputtered tantalumfilm. We have concluded, then, that there is an optimum amount of ionbombardment of a tantalum film surface to produce a Ta film having onlyminor residual stress (whether compressive or in tension). Processpressure appears to have the greatest effect of the variables tested. Itis believed that an increase in the process pressure leads to anincrease in ionization within the process chamber, which leads toincreased ion bombardment of the depositing film surface.

Example Three

The effect of the increase in ion bombardment of a depositing filmsurface, which can be achieved by increasing the DC offset bias voltageof the substrate onto which the film is deposited, is illustrated inFIG. 3. Graph 300 shows the residual stress 311 in dynes/cm² 310 as afunction of the AC bias power 320 in Watts. The corresponding substrateDC offset bias voltage ranges from about 0 V to about -150 V.

Example Four

When tantalum nitride films are produced, the structure of the tantalumnitride depends on the amount of nitrogen in the tantalum nitridecompound (film). FIGS. 4 and 5 show the chemical composition andresistivity of tantalum nitride films produced using Gamma sputteringand IMP sputtering techniques, respectively. The chemical composition(atomic nitrogen content) of the film is shown as a function of thenitrogen gas flow rate to the process chamber in which the TaN_(x) filmis produced.

FIG. 4, graph 400, shows the nitrogen content 410 of the Gamma-sputteredtantalum nitride film in atomic % 413, as a function of the nitrogenflow rate 416 in sccm to the process vessel. A two hundred (200) mmdiameter sample surface was Gamma sputter-deposited at a sample surfacetemperature of about 25° C., in an argon/nitrogen atmosphere, at apressure of about 1.5 mT, where the Argon gas feed was about 15 sccm andthe nitrogen flow rate 416 was as shown on graph 400. The "throw"distance between the tantalum target and the sample surface wasapproximately 250 mm. The DC power to the tantalum target was about 4kW.

In addition, graph 400 shows the resistivity 412 in μ Ω-cm 414 of thetantalum nitride film as the nitrogen content 413 increases. Theresistivity corresponds with the change in the tantalum nitridestructure, as indicated on Graph 400, where 402 represents β-Ta; 404represents bcc--Ta(N); 406 represents amorphous TaN_(x) ; and 408represents nanocrystalline fcc--TaN_(x) (x≈1).

FIG. 4 shows that when the atomic nitrogen content exceeds about 45% toabout 50%, the resistivity of the TaN_(x) film increases drastically (toabove 1,000 μ Ω-cm).

FIG. 6, graph 600, shows the residual film stress in dynes/cm² 602 of aGamma sputtered TaN_(x) film, as a function of the nitrogen flow rate tothe process chamber in sccm 604, and as a function of the substratetemperature at the time of film deposition, when the other processvariables are held at the values described with reference to FIG. 4.

Curve 610 represents the TaN_(x) film Gamma sputtered at a substratetemperature of about 25° C.; Curve 612 represents the TaN_(x) film Gammasputtered at a substrate temperature of about 250° C., and Curve 614represents the TaN_(x) film Gamma sputtered at a substrate temperatureof about 450° C.

Line 606 constructed at a nitrogen flow rate 604 of about 16 sccm,represents the atomic nitrogen content in excess of which theresistivity of the TaN_(x) film increases drastically (as illustrated inFIG. 4 for a nitrogen flow rate of 16 sccm). Thus, the gamma-sputteredTaN_(x) films having reduced residual compressive stress (in thedirection of arrow 608) occur at nitrogen contents at which theresistivity of the film is unacceptably high (greater than about 1,000 μΩ-cm). Looking at the residual film stress of TaN_(x) films having aresistivity lower than about 1,000 μ Ω-cm, it is evident that residualfilm stress can be reduced by increasing the substrate temperature atthe time of film deposition. This is in contrast with TaN_(x) filmshaving a resistivity higher than about 1,000 μ Ω-cm, where the residualfilm stress increases when the substrate temperature is higher duringfilm deposition. Considering this unexpected result, for Gamma sputteredfilms having a nitrogen content below about 45%-50%, it is preferable todeposit the TaN_(x) film at a substrate temperature of at least about250° C., and more preferably at a substrate temperature of at leastabout 350° C.

Example Five

FIG. 5 graph 500 shows the nitrogen content 510 of the reactiveIMP-sputtered TaN_(x) film in atomic % 513, as a function of thenitrogen flow rate in sccm 516 to the process chamber. A two hundred(200) mm diameter sample (substrate) surface was reactive IMPsputter-deposited at a sample surface temperature of about 25° C., in anargon/nitrogen atmosphere, at a pressure of about 40 mT, where Argon gasfeed was about 95 sccm (80 sccm to the process chamber feed and 15 sccmto the heat exchange surface) and the nitrogen flow rate 516 was asshown on graph 500. The DC power to the tantalum target was about 2 kW.The RF power to the IMP induction coil was about 1.5 kW. No offset biasof the substrate was used.

In addition, graph 500 shows the resistivity 512 in μ Ω-cm 514 of theIMP sputtered TaN_(x) film as the atomic nitrogen content 513 increases.The resistivity corresponds with the change in the tantalum nitridestructure, as indicated on Graph 500, where 502 represents β-Ta; 504represents bcc--Ta(N); 506 represents amorphous TaN_(x) ; and 508represents nanocrystalline fcc--TaN_(x) (x≈1).

FIG. 5 also shows that when the atomic nitrogen content exceeds about45%, the resistivity of the TaN_(x) film increases drastically (to above1,000 μ Ω-cm).

FIG. 7, graph 700, shows the residual film stress in dynes/cm² 702 of anIMP sputtered TaN_(x) film, as a function of the nitrogen flow rate tothe process chamber in sccm 704, for deposition on a substrate at atemperature of about 25° C., when the other process variables are heldat the values described with reference to FIG. 5.

Line 706, constructed at a nitrogen flow rate 704 of about 14-16 sccm,represents the atomic nitrogen content in excess of which theresistivity of the TaN_(x) film increases drastically (as illustrated inFIG. 5). We discovered that for IMP sputtered TaN_(x) films, in contrastwith the gamma sputtered films, it is possible to produce a film havingreduced residual stress at the lower nitrogen contents, where anacceptable resistivity can be obtained. Further, the IMP sputteredTaN_(x) film residual stress appears to remain relatively unaffected byan increase in the nitrogen content over the nitrogen content rangerepresented by the nitrogen flow rates illustrated in FIG. 7 (up toabout 60 atomic % nitrogen, based on FIG. 5).

By depositing the tantalum nitride film using the IMP sputtering methodwhich provides increased bombardment of the depositing film surface(over that obtained by the Gamma sputtering method), it is possible toproduce a TaN_(x) film having both an acceptable resistivity and reducedresidual film stress. This is because the IMP sputtered TaN_(x) filmstress remains relatively unchanged with increasing nitrogen content (incomparison with gamma sputtered TaN_(x) film stress which is stronglydependent on the nitrogen content of the film in the region where thefilm resistivity is acceptable).

The above described preferred embodiments are not intended to limit thescope of the present invention, as one skilled in the art can, in viewof the present disclosure expand such embodiments to correspond with thesubject matter of the invention claimed below.

We claim:
 1. A method of sputter depositing a tantalum film having adesired nominal residual film stress by tuning at least two processvariables which have an opposite effect on said residual film stress, toproduce said tantalum film having said desired nominal residual filmstress.
 2. The method of claim 1, wherein said tantalum film isdeposited using high density plasma sputtering.
 3. The method of claim1, wherein said tantalum film comprises body centered cubic tantalum. 4.The method of claim 1, wherein a crystalline structure of said tantalumfilm is β tantalum.
 5. The method of claim 1, wherein an increase in anominal value of one of said at least two process variables increasessaid deposited film residual tensile stress, while an increase in anominal value of another of said at least two process variablesincreases said deposited film residual compressive stress.
 6. A methodof sputter depositing a tantalum film having a desired nominal residualfilm stress by tuning a combination of film deposition process variablesselected from the group consisting of process chamber pressure,substrate DC offset bias voltage, power to a sputtering target, power toan ionization source, and substrate temperature.
 7. The method of claim6, wherein said film is deposited by tuning said process variables toprovide a nominal residual film stress ranging between about 1×10⁺¹⁰dynes/cm² and about -2×10⁺¹⁰ dynes/cm².
 8. A method of sputterdepositing a tantalum nitride film having a desired nominal residualfilm stress by tuning at least two process variables which have anopposite effect on said residual film stress, to produce said tantalumnitride film having said desired nominal residual film stress.
 9. Themethod of claim 8, wherein said tantalum nitride film is deposited usingreactive high density plasma sputtering.
 10. The method of claim 9,wherein said tantalum nitride film comprises at least 30 atomic %nitrogen.
 11. The method of claim 10, wherein said nitrogen content isless than 60 atomic % nitrogen.
 12. The method of claim 8, wherein anincrease in a nominal value of one of said at least two processvariables increases said deposited film residual tensile stress, whilean increase in a nominal value of another of said at least two processvariables increases said deposited film residual compressive stress. 13.A method of sputter depositing a tantalum nitride film having a desirednominal residual film stress by tuning a combination of film depositionprocess variables selected from the group consisting of process chamberpressure, substrate DC offset bias voltage, power to a sputteringtarget, power to an ionization source, and substrate temperature. 14.The method of claim 13, wherein said film is deposited by tuning saidprocess variables to provide a nominal residual film stress rangingbetween about 1×10⁺¹⁰ dynes/cm² and about -2×10⁺¹⁰ dynes/cm².